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   难度：Easy
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   <h1 class="question_title">
    463. Island Perimeter
   </h1>
   <p>
    You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water.
   </p>
   <p>
    Grid cells are connected horizontally/vertically (not diagonally). The grid is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells).
   </p>
   <p>
    The island doesn't have "lakes" (water inside that isn't connected to the water around the island). One cell is a square with side length 1. The grid is rectangular, width and height don't exceed 100. Determine the perimeter of the island.
   </p>
   <p>
    &nbsp;
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   <p>
    <b>
     Example:
    </b>
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   <pre>
<strong>Input:</strong>
[[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

<strong>Output:</strong> 16

<strong>Explanation:</strong> The perimeter is the 16 yellow stripes in the image below:

<img src="https://assets.leetcode.com/uploads/2018/10/12/island.png" style="width: 221px; height: 213px;">
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   <h1 class="question_title">
    463. 岛屿的周长
   </h1>
   <p>
    给定一个包含 0 和 1 的二维网格地图，其中 1 表示陆地&nbsp;0 表示水域。
   </p>
   <p>
    网格中的格子水平和垂直方向相连（对角线方向不相连）。整个网格被水完全包围，但其中恰好有一个岛屿（或者说，一个或多个表示陆地的格子相连组成的岛屿）。
   </p>
   <p>
    岛屿中没有&ldquo;湖&rdquo;（&ldquo;湖&rdquo; 指水域在岛屿内部且不和岛屿周围的水相连）。格子是边长为 1 的正方形。网格为长方形，且宽度和高度均不超过 100 。计算这个岛屿的周长。
   </p>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     示例 :
    </strong>
   </p>
   <pre><strong>输入:</strong>
[[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

<strong>输出:</strong> 16

<strong>解释:</strong> 它的周长是下面图片中的 16 个黄色的边：

<img src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/10/12/island.png">
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